United States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,891,142
`
`Eggers et al.
`
`[45] Date of Patent:
`
`Apr. 6, 1999
`
`US005891142A
`
`[54] ELECTROSURGICAL FORCEPS
`
`FOREIGN PATENT DOCUMENTS
`
`[75]
`
`Inventors: Philip E_ Eggers Dublin. Andrew R.
`Eggers, Ostrander, both of Ohio
`
`[73] Assignee: Eggers & Associates, Inc., Dublin,
`Ohio
`
`[21] Appl. No.: 878,400
`.
`.
`Flled‘
`
`[22]
`
`Jun‘ 18’ 1997
`Related U.S. Application Data
`
`[63]
`
`C0ntinuation—in—part of Ser. No. 761,591, Dec. 6, 1996,
`aband0ned_
`
`Int. Cl.6 ..............................
`[51]
`[52] U-S- CL
`[58] Field Of Search
`7
`[59]
`
`.
`References Clted
`US, PATENT DOCUMENTS
`
`A61B 17/39
`606/51; 606/52
`606/50-52, 43
`
`3,685,518
`4,274,413
`4,492,231
`
`8/1972 Beuerle et al.
`6/1981
`1/1985
`
`...................... .. 606/51
`
`............... .. 606/52
`
`Eiiropean Pat. Off.
`12/1992
`517243
`Primary Examiner—Lee Cohen
`Attorney, Agent, or FL'rm—Mueller and Smith, LPA
`[57]
`ABSTRACT
`Surgical forceps Which are configured having oppositely
`disposed tissue grasping surfaces at
`the tip regions of
`corresponding tines. An electrically insulative spacer assem-
`bly is positioned on and supported from at least one of the
`tissue grasping surfaces to space the tissue contacting sur-
`faces apart an optimized distance, T, when the tines are in a
`Subsmntlally Ckjsed OnemanOn' A.pretCr.red’ Stflp torm .Ot
`spacer assembly formed of an electrically insulative material
`is employed and improved current paths are defined between
`the grasping Surfaces to derivc an eflicient and efl~eCfiVC
`hemostasis substantially Without sticking of tissue to the
`surfaces. The geometric configuration of the spacer regions
`functions to enhance cleanability of the forceps and the tines
`of the forceps additionally are formed with side and nose
`surfaces at
`the tip regions having elfective side surface
`current delivery areas improving forceps performance when
`used in a coagulative painting modality,
`
`87 Claims, 13 Drawing Sheets
`
`ETHICON ENDO-SURGERY, INC.
`
`EX. 1007
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`1
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`Apr. 6, 1999
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`Sheet 1 of 13
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`5,891,142
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`U.S. Patent
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`Apr. 6, 1999
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`5,891,142
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`Apr. 6, 1999
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`PRIOR ART
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`PRIOR ART
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`Sheet 13 of 13
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`PRIOR ART
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`14
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`5,891,142
`
`1
`ELECTROSURGICAL FORCEPS
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is a continuation-in-part of United States
`application for patent Ser. No. 08/761,591, filed Dec. 6,
`1996, entitled “Electrosurgical Forceps”, now abandoned.
`STATEMENT REGARDING FEDERALLY
`SPONSORED RESEARCH
`
`1
`
`Not applicable.
`BACKGROUND OF THE INVENTION
`.
`.
`.
`.
`Surgical procedures necessarily involve the transection of
`vessels as surgeons seek to explore, remove, or repair tissue
`defined systems. Transcction is carried out with a variety of
`cutting instruments ranging from a cold scalpel to electro-
`surgical devices. As such vessels are cut, it generally is
`necessary to accommodate bleeding by microsurgical or ‘
`similar approaches, or where smaller vessels are
`encountered, by a sealing and congealing procedure. This
`latter procedure typically is carried out by heating the
`involved tissue and fluids through the application of elec-
`trical current at RF frequencies developed by an electrosur-
`gical generator. Effective sealing of smaller vessels is impor-
`tant to surgical procedures, inasmuch as even a small blood
`flow not only can obscure the surgeon’s field of view, but
`
`also may accumulate with the risk of hematoma or signifi-
`cant blood loss.
`
`3
`
`While a variety of electrosurgical instruments have been
`developed to achieve hemostasis, many are of marginal
`effectiveness for certain surgical tasks, particularly those
`involving small vessels and small, highly localized tissue
`regions of interest. To carry out such somewhat delicate
`surgical procedures requisite to such regions, practitioners
`typically employ forceps, instruments of common utility
`which, in effect, represent a thin extension of the thumb and
`forefinger function of the surgeon. Forceps generally serve
`to provide a tissue or vessel grasping function, having
`working ends or tip portions which may be of diminutive
`dimension enabling the surgeon to locate and grasp small
`vessels which have a tendency to retract into tissue follow-
`ing their being cut. By applying bipolar, RF current from a ,
`noted electrosurgical generator across the outer working end
`tips of the forceps, a seahng or congealing of tissue or
`vessels can be achieved without substantial risk to adjacent
`tissue. In effect, the well defined tips of the bipolar forceps
`provide a more precise attainment of hemostasis.
`Another surgcal application for bipolar forceps has been
`referred to as “coagulative painting” where typically, the
`side surfaces of the electrically active tip regions of the
`forceps’ tines are drawn over the surface of membranous
`tissue such as the mesentery. Done properly, this action
`congeals the small, microvessels within such thin tissues.
`Electrosurgically driven forceps heretofore made avail-
`able to surgeons, however, have exhibited operational
`drawbacks, which, in turn, have compromised their surgical
`effectiveness. To effectively carry out hemostasis, the elec-
`trically operative tips of the forceps should efficiently con-
`duct a proper current flow through the tissue grasped. When
`that current is insu icient, coagulation of the tissue or vessel
`is compromised. When the current is excessive, correspond-
`ingly excessive heating occurs with a potential
`for the
`generation of damaging electrical arcing. Excessive heating
`also results in the phenomenon of tissue and blood coaguluni
`
`2
`sticking to the surface of the instrument. This results in the
`development of a layer of increased electrical impedance
`between the electrodes of the instrument and that tissue
`which may subsequently be grasped for the purpose of
`treatment. Additionally, such sticking tissue evokes a dis-
`ruption of the coagiilated surface which,
`in itself, may
`compromise the intended hemostatic effect. Consequently,
`bipolar forceps designs have been seen to incorporate highly
`polished electrode surfaces for the purpose of reducing the
`extent of tissue sticking as well as to facilitate their cleaning
`when sticking does occur. Unfortunately, when such modi-
`fication of the forceps is carried out, the original grasping
`function of the forceps is substantially compromised.
`Another problem encountered with the use of bipolar
`forceps of conventional design has been associated with
`their use in conjunction with thin tissue. As such tissue is
`grasped between the opposed bipolar electrodes of the
`instruments, only a low tissue related impedance is wit-
`nessed by the electrosurgical generator associated with the
`instrument, which conventionally reacts to decrease its out-
`put
`toward zero as tissue impedance approaches a zero
`value.
`
`Use of the bipolar forceps also becomes problematic in
`conjunction with the noted “coagulative painting” procedure
`where the side surfaces of the instrument are drawn across
`the surface of membranous tissue. The electrical model
`involved in this procedure is one wherein current is caused
`to flow from the side surface of one tine, thence across a thin
`layer of tissue to the oppositely disposed spaced apart
`electrically operant tine. lhis calls for maintenance of the
`spacing between the two tines to avoid short circuiting the
`system and for a control over what is, in effect, a moving line
`source of heat applied to the alfected tissue. Very often, a
`misjudgment may lead to the tearing of tissue in the proce-
`dure. Of course,
`it also is necessary for the surgeon to
`maintain a spacing between tine electrodes of the instrument
`to achieve requisite performance.
`Approaches to minimizing the phenomenon of tissue
`sticking to the operative tips of bipolar forceps have been
`advanced by the medical instrument industry. For example,
`designs have propounded the use of forceps’ legs having
`cross—sectional areas and which exhibit conductivity sulfi-
`ciently high to maintain electrically operative portions for
`the instruments below threshold temperatures considered to
`evoke tissue sticking. Similarly,
`the temperature of the
`grasping tips of the forceps has been reduced by enlarging
`the cross—sectional radii of the forceps sufficiently to main-
`tain current density and resultant tissue heating below the
`threshold temperature evoking sticking. See in this regard,
`U.S. Pat. Nos. 3,685,518; 4,492,231; and 5,196,009.
`However, the election of a large cross—sectional area at the
`grasping tips of the forceps for purposes of heat conduction
`compromises the basically sought precision of the forceps
`type instrument with respect
`to grasping and localized
`coagulation of smaller blood vessels, e.g. vessels smaller
`than about 1 mm in diameter.
`
`An approach to limiting the heating of the tissue or vessel
`being coagulated with bipolar forceps has been to utilize a
`layer of a ceramic material having a thermal conductivity
`much lower than that of the metal used in the structure of the
`forceps. U.S. Pat. No. 5,151,102 describes such an arrange-
`ment wherein a plurality of silver filled epoxy electrodes are
`embedded within the ceramic coatings. However, Joulean
`heating with bipolar systems occurs within the tissue which,
`for such arrangements, has no effective pathway through
`which to dissipate, resulting in an enhancement of the
`sticking problem which now occurs at the ceramic layer.
`
`15
`
`

`
`5,891,142
`
`3
`To regain the originally desired grasping feature of
`forceps, the utilization of a roughened or tooth-like surface
`in conjunction with the electrically operative ends of the
`forceps has been proposed as represented in US. Pat. Nos.
`5,330,471 and 5,391,166. By disposing a layer of insulation
`on the teeth of one or both of the grasping surfaces, electrical
`current only passes along the sides of the electrode surfaces
`which are outwardly disposed from the grasping surfaces.
`Thus, the utility of the forceps is compromised to the extent
`that only thicker tissues can be grasped and coagulated
`efficiently. In general, serrated or multi—pyramidally config-
`ured grasping surfaces prove dillicult to clean during surgery
`due to the recesses and grooves which tend to trap tissue
`debris and coagulum.
`U.S. Pat. No. 5,403,312 describes a combination of an
`electrosurgical forceps form of instrument which addition-
`ally carries out a stapling function. Intended for the grasping
`of thicker tissue components, the device described employs
`operative forceps tips with mutually offset or staggered
`electrode regions suitable for more extended thickness’ of
`tissue as opposed to thin tissue. By mounting the electrode
`regions within a plastic support member, an otherwise
`desired feature for heat removal is compromised permitting
`the electrodes to reach temperatures during tissue coagula-
`tion that can exceed sticking threshold temperatures with the
`noted undesirable cleaning requirements.
`Some investigators have proposed the utilization of tem-
`perature sensors such as thermocouples which are incorpo-
`rated within the bipolar forceps instruments. Propounded in
`us. Pat. Nos. 5,443,463; 4,938,761; and 5,540,684, the
`approach requires that a special control system be provided
`which precludes the utilization of the ubiquitous conven-
`tional electrosurgical generator currently available in oper-
`ating theaters throughout the world. Further, the otherwise
`simple construction of the forceps must be abandoned to a
`less desirable, highly complex instrumentation with such an
`approach.
`BRIEF SUMMARY OF THE INVENTION
`
`The present invention is addressed 0 improved surgical
`forceps and the methods by which they may be used with the
`bipolar outputs of eleetosurgical generators of conventional
`design and which achieve a highly e icient hemostasis of
`grasped tissue or vessels. This result is realized through the
`development of current paths exhibiting desirable current
`densities and more ideal current path configurations. These
`forceps employ electrically insulative spacer regions or
`assemblies in conjunction with the mutually inwardly facing
`electrically conductive tissue grasping surfaces of the two
`movable tines of the instruments. The spacer arrangement
`serves to space the tissue grasping surfaces apart an opti-
`mum distance, T, when substantially in a closed orientation.
`Configurations for this spacer assembly achieve the ideal
`current path lengths developing hemostasis without
`the
`presence of recurrent sticking phenomenon. This avoidance
`of sticking is achieved While the grasping feature of the
`forceps is not compromised and an ability to clean them
`effectively and e iciently is achieved.
`These spacer regions or assemblies of the present inven-
`tion then provide for an importantly improved grasping of
`tissue even though the exposed metal portions of the grasp-
`ing surfaces are made to have smooth surfaces in order to
`minimize sticking to tissue or coagulum and to facilitate
`their cleaning when tissue debris or coagulum does accu-
`mulate.
`
`In a preferred embodiment for the forceps, the two tines
`thereof are formed having inwardly disposed and highly
`
`,
`
`_
`
`4
`polished electrically conductive tissue grasping surfaces.
`Located upon one of these surfaces, for example, is an array
`of very thin electrically insulative regularly spaced discrete
`strips of electrically insulative material such as alumina.
`These strips are quite diminutive and barely tactilely
`discernible, and achieve the noted spacing distance, T,
`having a minimum value of about 0.005 inch. Avariety of
`configurations for the spacer regions or assemblies are
`disclosed providing for the achievement of the noted opera-
`tional improvements.
`Preferably, the forceps of the invention are fabricated such
`that each tine incorporates a thermally conductive material
`such as copper in an amount su icient
`to maintain the
`temperature at the tip region during typical use below about
`60° C. to 85° C. This temperature regime for the forceps is
`predicated upon a conventional duty cycle of use and is
`achieved with practicality through the use of laminar com-
`posites of thermally conductive copper and mechanically
`stronger, particularly, higher modulus stainless steel. The
`electrically insulative spacers are fashioned, for example, of
`alumina, which readily is deposited upon one or both of the
`inwardly facing stainless steel surfaces. Biocompatibility of
`the entire forceps assemblage is maintained through an
`electro-deposited biocompatible metal coating such as chro-
`mium which coats both the stainless steel and copper
`laminate while not a ecting the alumina spacer.
`Another aspect of ie invention looks to an improvement
`of that feature of surgical forceps employed to achieve the
`noted coagulative painting.
`I11 this regard,
`the tines are
`formed having a generally rectangular cross section at their
`tip regions. This cross section enhances the available current
`path deriving area of the side surfaces for purposes of
`coagulative painting. Additionally, the forceps may be made
`with relatively blunt nose components to permit a more
`localized but still effective coagulative painting.
`Other objects of the invention will, in part, be obvious and
`will, in part, appear hereinafter.
`The invention, accordingly, comprises the apparatus and
`method possessing the construction, combination of
`elements, arrangement of parts, and steps which are exem-
`plified in the following detailed description.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a perspective View of a bipolar forceps coupled
`by a bipolar cable to the bipolar terminals of an electrosur-
`gical generator;
`FIG. 2 is a partial sectional view of a prior art forceps;
`FIG. 3 is a sectional view taken through the plane 3—3 in
`FIG. 2;
`FIG. 4 is a partial sectional view of another forceps of the
`prior art;
`FIG. 5 is a graph relating load impedance to normalized
`power for two typically encountered electrosurgical genera-
`tors;
`FIG. 6 is a partial sectional view of forceps of the prior
`art;
`
`FIG. 7 is a sectional View taken through the plane 7—7
`seen in FIG. 6;
`FIG. 8 is a partial sectional view of one embodiment of
`forceps and method of their use according to the invention
`with portions exaggerated to reveal structure;
`FIG. 9 is a sectional view taken through the plane 9—9 in
`FIG. 8;
`FIG. 10 is a plan view of a tip region of a tine of the
`forceps described in FIG. 8;
`
`16
`
`

`
`5,891,142
`
`5
`FIG. 11 is a partial sectional view of the forceps shown in
`FIG. 8 with a full closure orientation;
`FIG. 12 is a partial sectional View of a preferred embodi-
`ment of the invention with portions exaggerated to reveal
`structure;
`FIG. 12Ais a partial sectional view according to FIG. 12
`showing a laminar composite structure of tine components;
`FIG. 13 is a sectional view taken through the plane
`13—13 in FIG. 12;
`FIG. 14 is a plan view of the forceps of FIG. 12 without
`exaggerated dimension;
`FIG. 15 is a plan view of a tip region of a tine of the
`forceps of another embodiment of the invention;
`FIG. 16 is a sectional view of forceps incorporating the tip
`region shown in FIG. 15;
`FIG. 17 is a plan view of the tip region of a tine of another
`embodiment of forceps according to the invention;
`FIG. 18 is a plan view of the tip region of a tine of another
`embodiment of forceps according to the invention;
`FIG. 19 is a sectional view taken through the plane
`19—19 in FIG. 18;
`FIG. 20 is a partial sectional View of another embodiment
`of forceps according to the invention;
`FIG. 21 is a partial sectional view of a tooth-like structure
`seen in FIG. 20;
`FIG. 22 is a partial sectional View of another embodiment
`of the invention with portions exaggerated to reveal struc-
`ture,
`FIG. 23 is a partial sectional View of one tip region of the
`embodiment of FIG. 22;
`FIG. 24 is a partial sectional View of the embodiment of
`FIG. 22 showing tissue grasping surface spacing;
`FIG. 25 is a partial sectional view of another embodiment
`of the invention with portions exaggerated to reveal struc-
`ture;
`FIG. 26 is a partial sectional view of the embodiment of
`FIG. 25 showing relative grasping surface spacing;
`FIG. 26A is a partial sectional view of the embodiment of
`FIG. 25 showing an alternate arrangement or an electrically
`insulative spacer assembly;
`FIG. 27 is a pictorial representation of the side surface /
`mode and method of utilization of forceps according to the
`invention;
`FIG. 28 is a sectional View of forceps according to the
`invention employed in the manner shown in FIG. 27;
`FIG. 29 is a sectional view of forceps according to the _
`prior art being utilized in the mode shown in FIG. 27;
`FIG. 30 is a partial sectional view of forceps according to
`the invention being used in another version of the mode
`described in connection with FIG. 27;
`FIG. 31 is a sectional view of the tip region of forceps
`according to the invention for supporting a geometric analy-
`sis thereof; and
`FIG. 32 is a sectional view of the tip region of forceps
`according to the prior art for supporting a comparative
`analysis with respect to FIG. 31.
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`The bipolar electrosurgical forceps of the invention per-
`form in conjunction with conventional electrosurgical gen-
`erators having bipolar outputs. These generators are coni-
`
`6
`mon in essentially all operating theaters and generate radio
`frequency voltage or power typically in response to the
`depression of a foot pedal on the part of the surgeon.
`Referring to FIG. 1, such a generator is represented gener-
`ally at 10. Device 10 provides a bipolar, as opposed to
`monopolar, output at receptacles 12 and 14. The applied
`voltage level or power level at receptacles or outputs 12 and
`14 may be selected by the user by adjustment of a control
`knob as at 16. Activation of the power outputs at receptacles
`12 and 14 is provided by a foot pedal switch 18 wl1icl1 is
`connected to generator 10 via a cable 20. Outputs 12 and 14
`are coupled to the respective plugs 22 and 24 of a bipolar
`cable 26,
`the opposite end of which terminates in two
`receptacles 28 and 30. Receptacles 28 and 30 are electrically
`connected with corresponding connector posts (not shown)
`which are recessed within a connector housing 32 of a
`bipolar forceps represented generally at 34. Forceps 34 are
`formed of two, somewhat resilient thermally and electrically
`conductive tines or support members 36 and 38 which are
`mounted within the connector housing 32 and extend lon-
`gitudinally outwardly therefrom in a mutually angularly
`oriented fashion to respective tip regions 40 and 42.
`Inwardly disposed in mutual facing relationship at the tip
`regions 40 and 42 are electrically conductive fiat tissue
`grasping surfaces represented, respectively, at 44 and 46.
`These surfaces 44 and 46 are coated with an electrically
`insulative material such as alumina, which, in turn, for the
`present embodiment is gang ground to produce a sequence
`of stripes or parallel bands of alternating electrically con-
`ductive metal and electrically insulative material. The
`stripes for surfaces 44 and 46 are mutually aligned such that
`when the tines 38 and 36 are squeezed to a closed or tissue
`grasping orientation, the electrically conductive stripes or
`bands at surfaces 44 and 46 move toward a mutual contact
`_ while the electrically conductive surfaces adjacent to them
`are mutually aligned such that a directly confronting current
`path through tissue may be developed between them. To
`provide for bipolar performance, the surfaces of tines 36 and
`38 located rearwardly of the tip regions 40 and 42 are coated
`with an electrically insulative material such as a nylon. In
`general, forceps as at 34 are constructed to be sterilizable by
`autoclaving or the like. Tines 36 and 38 may be mounted
`within the connector housing 32 using an epoxy potting
`agent within the interior of a plastic shell. Other mounting
`techniques will occur to those who are art-skilled.
`Looking to FIGS. 2 and 3, an approach to the design of
`bipolar surgical forceps in the past
`is revealed with the
`purpose of analysis. In the figure, forceps 52 are fashioned
`having two electrically conductive tines 54 and 56,
`the
`rearwardly disposed portions of which are coated with an
`electrically insulative polymeric material as shown,
`respectively, at 58 and 60. The electrically operant
`tip
`regions of tines 54 and 56 are shown, respectively at 62 and
`64. Tip regions 62 and 64 are configured having flat bare
`metal and polished,
`tissue grasping surfaces shown,
`respectively, at 66 and 68, and the cross-sections of the tip
`regions are somewhat semi—circular in configuration. Sur-
`faces 66 and 68 are shown grasping tissue 70. Because of the
`smooth, all metal contact surfaces 66 and 68, upon actuation
`of the electrosurgical system by, for example, closing a
`switch such as at foot pedal 18 (FIG. 1), a radio frequency
`voltage difference is applied across the tip regions 62 and 64,
`and electrical current is caused to flow, for the most part,
`through the portion of tissue 70 in contact with the surfaces
`66 and 68. This heats such tissue or blood vessel 70
`sufficiently to carry out its thermocoagulation. While the
`provision of smooth grasping surfaces 66 and 68 functions
`
`17
`
`

`
`5,891,142
`
`7
`advantageously to minimize the sticking of tissue or blood
`coagulum to such surfaces,
`their smoothness defeats the
`basic function of forceps which is to grasp tissue and hold
`it. Often, the tissue or blood vessel grasped at 70 slips out of
`the engagement before coagulation can be carried out. While
`the current passing through tissue 70 directly confronts it
`and passes therethrough to carry out Joulean heating as
`represented by dashed current flux lines 72,
`the larger
`contact area has been observed to promote higher current
`levels which,
`in turn,
`lead to higher heating rates which
`promotes the sticking of tissue or coagulum to the grasping
`surfaces 66 and 68. Often, when the tip regions 62 and 64 are
`opened to release the thus-coagulated tissue or vessels,
`sticking causes an avulsion of the sealing layer of a coagu-
`lum to somewhat defeat the procedure. In addition, even a
`very thin layer of desiccated tissue residue or blood coagu-
`lum will introduce a large electrical resistance at the inter-
`face between the tip regions 62 and 64 and any subsequent
`tissue or blood vessel which is grasped. This detracts from
`the operational capability of the instrument and calls for
`cleaning or changing instruments during the surgical proce-
`dure. Where a very thin layer of tissue is grasped or a very
`small vessel is grasped between the tip regions 62 and 64, a
`reduced load impedance is witnessed by the associated
`electrosurgical generator as at 10. It is the characteristic of
`such generators that as such load impedance reduces and
`approaches zero, the output voltage of the generator will
`decrease and approach zero volts to the extent
`that no
`voltage di ‘erence will be applied across the tip regions 62
`and 64. It follows that no current for carrying out Joulean
`heating will flow through the grasped tissue or blood vessel
`and no coagulation can be achieved.
`Particularly where miniature forceps are utilized, the bare
`tissue grasping surfaces 66 and 68 may be driven into mutual
`contact to cause a short circuit. This is illustrated in cori-
`nection with FIG. 4 where a smaller or more diminutive
`tissue component 74 is seen being grasped between the
`grasping surfaces 66 and 68, however, those surfaces are in
`contact with each other in the vicinity of location 72 to cause
`a short circuiting. Of course, arcing is a possibility as the
`surfaces closely approach each other. Note that the electri-
`cally insulative coatings 58 and 60 are in contact under this
`geometry but often will not prevent the short circuiting.
`To achieve a performance of bipolar forceps which
`approaches optimal, it is necessary to appreciate the opera-
`tional characteristics of the ubiquitous electrosurgical gen-
`erators which are present in essentially all operating theaters.
`VVhile numerous brands of these generators are extant
`throughout the world, they, for the most part, have a some-
`what similar output characteristic. Referring to FIG. 5,
`normalized curves relating load impedance to power repre-
`sentative of two conventionally encountered electrosurgical
`generators are revealed at 80 and 82. Curves 80 and 82 have
`similar shapes at relatively lower load impedances and, as in
`the case of most electrosurgical generators on the market, a
`maximum power output is achieved in the neighborhood of
`100 ohms. As load impedance increases beyond peak value,
`then as evidenced by the curves,
`the normalized power
`reduces and will fall olf with a characteristic somewhat
`associated with each individual generator. Thus, if the load
`impedance increases excessively, power falls off and inef-
`ficient coagulation is the result. Similarly, as the load imped-
`ance approaches zero, to the point of shorting out, no power
`is available also. Efficient coagulation is found to occur with
`load impedances somewhere in the range of 10 to 150 ohms,
`and the goal of the instant design is to achieve efilcient
`coagulation for essentially most circumstances encountered
`in surgery with bipolar forceps while avoiding a sticking
`phenomena.
`
`8
`it also
`With the above characteristic curves in mind,
`tissue
`should be observed that
`the electrically operant,
`engaging grasping regions of the forceps will perform in
`conjunction with a load resistance which,
`in its simplest
`form, may be expressed as follows:
`
`PL
`A
`
`(1)
`
`where A is the total area through which current can flow, i.e.
`it is the area which the current delivering surface confronts
`including that region which may flare out from the edge of
`an electrode defining portion of the forceps tissue contacting
`surface. L is the length of the pathway taken by the current,
`and p is the characteristic resistivity of the tissue engaged.
`The undesirable phenomena of sticking is not necessarily
`a result of the total power delivered from the forceps to the
`tissue but is a function of the power density or power per unit
`area delivered from the electrode surfaces. Thus,
`if the
`power density is controlled at the operational surfaces of the
`instruments, sticking may be minimized by an arrangement
`where current is being distributed over larger surface areas.
`A further aspect is concerned with the efficiency of deliv-
`ering this current into the tissue to achieve a Joulean heating
`of it. This delivery should be the most efficient for carrying
`out coagulation and sealing. Coagulation should occur with
`the least amount of dwell time and be so localized as not to
`adversely affect tissue which is adjacent that being coagu-
`lated or sealed. These aspects are in the interest of both the
`patient and the surgeon.
`Investigators have endeavored to overcome the poor
`grasping aspect and tendency to evoke sticking occasioned
`with bare surface bipolar forceps by turning to the expedient
`of coating the tissue grasping surfaces of the tip regions of
`the forceps. Looking to FIGS. 6 and 7, such an arrangement
`is depicted in sectional fashion.
`Ir1 FIG. 6, the forceps is
`represented in general at 84 having tines 86 and 88 with
`respective tip regions 90 and 92. Tip regions 90 and 92 have
`respective grasping surfaces 94 and 96 which, at least in
`part, are covered with a continuous coating of electrically
`insulative material shown, respectively, at 98 and 100.
`Continuous coatings 98 and 100 may be provided, for
`example, as a ceramic and thus incorporate a frictional
`aspect improving the tissue grasping ability of the device 84.
`In this regard, a component of tissue is shown in the
`drawings at 102. FIG. 7 reveals, however, that by so coating
`the grasping surfaces with a ceramic insulator, current flow
`is restricted essentially to the outer edges of the tip regions
`90 and 92. Such a current flux path arrangement is in FIG.
`7 at dashed lines 104 and 106. While the arrangement
`achieves improved grasping and reduced heating with a
`corresponding reduced likelihood of the sticking of tissue or
`coagulum to the grasping surfaces, if the tissue or blood
`vessel 102 has a small thickness, then little or no electrical
`contact may be achieved at the tip region edges with the
`result of little or no current llow. Such low current llow
`lowers the efficiency of requisite Joulean heating of the
`tissue to achieve coagulation. However, if the tissue 102 is
`relatively thick, then sufficient heating and coagulation may
`be achieved because of the added contact of electrode
`surface with tissue.
`Referring to FIGS. 8-10, a depiction of an initial embodi-
`ment of forceps according to the invention is portrayed with
`some exaggeration of scale to facilitate the description
`thereof. The forceps are represented generally at 110 and
`include two tines 112 and 114 which are electrically con-
`ductive and extend, respectively, to tip regions 116 and 118.
`Rearwardly of the tip regions 116 and 118, the tines 112 and
`
`18
`
`

`
`5,891,142
`
`9
`114 are coated, respectively, with an electrically insulative
`coating shown, respectively, at 117 and 119. Coatings 120
`and 122 preferably are formed of nylon, while the tines 112
`and 114 are formed of a metal, for example, a 300 or 400
`series stainless steel, nickel, tungsten, copper, or alloys of
`such metals. In a preferred arrangement, the tines 112 and
`114 are formed of a laminar composite which combines a
`thermally conductive metal such as copper with a biocor11-
`patible and higher modulus metal such as stainless steel. The
`higher modulus of the stainless steel layer a ords mechani-
`cal characteristics which more closely matc 1 conventional
`stainless steel forceps (e.g., forceps closure force and for-
`ceps tine deflection during grasping). In general, the stain-
`less steel is inwardly facing to establish the base for tissue
`grasping surfaces.
`Inasmuch as certain of the thermally
`conductive materials such as copper are not biocompatible,
`the composites preferably are covered with an electro-
`deposited layer of a compatible material such as chromium.
`In addition, the inwardly facing stainless steel member (on
`embodiments with